Glycidyl esters are an important starting material in the chemical industry. The glycidyl esters are typically prepared by reaction of epichlorohydrin with a carboxylic acid in the presence of catalyst and subsequent dehydrochlorination of the resulting mixture of chlorohydrin esters followed by their separation. In particular the glycidyl esters of branched carboxylic acids and epoxy specialties are of commercial importance, which find use in the production of high-grade alkyd resins, polyester resins, acrylic resins, and a variety of other resins, and also as reactive diluent. Of particular interest are the glycidyl esters commercialized under the CARDURA™ trademark, which have been used for decades as a building block for automotive OEM, Refinish and CED coatings. The Glycidyl Ester of Versatic™ acid exhibits UV stability, acid etch resistance and a unique ability to create high solids low viscosity polymers with good substrate wetting.
Of similar interest is the 1,2-epoxyethyl carboxylate, for instance the product of the epoxidation of vinyl pivalate and in particular the product of the epoxidation of a vinyl ester of a branched carboxylic acid. Such esters are commercially available under the VEOVA™ trademark.
Epoxidation of vinyl esters or allyl esters is uncommon. According to the literature it is possible to epoxidize vinyl acetate by using a Ti-MWW/H2O2 catalytic system (“Epoxidation of Various Functionalized Olefins by a Ti-MWW/H2O2 Catalytic System”, by LI Ningnin et al in Chin J Catal, 2008, 29(2): 102-104). From this reference it is known that the epoxidation of a C═C bond is more difficult when the C═C bond is connected to groups having a high electron drawing group. The epoxidation of vinyl esters is even more difficult than the epoxidation of allyl esters. This is because the C═C bond in the vinyl group is conjugated with the C═O bond or adjacent to the C—O bond, which makes it electronically more deficient than the C═O bond in the allyl group. The conversion and product selectivity of, for example, allyl acetate epoxidation were higher than that of vinyl acetate epoxidation.
In “Synthesis of some epoxy vinyl monomers by epoxidation with peracetic acid” by F. C. Frostick et al, JACS, 81 (1958) 3350, the epoxidation of vinylpent-4-enoate is described, resulting in the production of vinyl 4,5-epoxypentanoate. The vinyl group is not epoxidized. In the same report reaction constants are given for reaction esters (vinyl acetate, ethyl acrylate, allyl acetate, allyl ether). As can be concluded from the reaction constants, epoxidation of esters is very slow (in some cases does not happen like vinyl acetate and ethyl acrylate).
In EP0618202 various olefins such as 4-vinylbenzoic acid, styrylacetic acid, trans-3-hexenoic acid, trans-2-hexenoic acid and allyl alcohol are epoxidized by contact with a source of oxygen and a Mn complex, such as a binuclear manganese complex, in which the Mn is co-ordinated to an N-containing ligand such that there is a ratio of Mn to co-ordinated N atoms of 1:3. Suitable olefins include compounds with from 2 to 50 carbon atoms, such as those having from 3 to 20 carbon atoms. They may be selected from mono- or multi-substituted and unsubstituted, branched or unbranched alkenes and arylalkenes. Substitution of the alkenes may be in the form of hetero atom functional groups including those of halo, cyano, carboxylate, sulphate, phosphate, amino, hydroxyl, nitro, alkoxy, acyloxy and combinations thereof. When the epoxidation process is conducted in an aqueous media, best results are obtained on olefins with water-soluble groups such as those with carboxylate and hydroxyl units, e.g. vinylbenzoic acid, styrylacetic acid and hexenoic acid. This reference does not disclose the epoxidation of vinyl carboxylates or allyl carboxylates.
The inventors set out to find an alternative route to glycidyl esters of carboxylic acids that does not rely on epichlorohydrin. Such an alternative route has been found. Moreover, this new route also opens the possibility of preparing epoxyethyl esters of carboxylic acids which will find use in the same applications where the glycidyl esters are used.
The present invention provides an attractive route to such products.